The invention relates to electron beam printers and more particularly to the imaging cartridge and the electrical path used to control the high frequency alternating potential, which relates an electrical discharge, which produces electrons. Particularly, the invention uses a shielding conductive plane which acts as an intermediary layer between the electrically active area and the mechanical substrate of an electron beam print cartridge. This intermediary layer is electrically insulated from the active area and the mechanical substrate by other intermediary layers of insulating material. The imaging electron beams are generated in the active area of the print cartridge through the application of high voltage AC bursts between about 160 and 280 volts peak to peak (and all narrower ranges within this broad range) at RF frequencies between about 2.0 and 10.0 mHz (and all narrower ranges within this broad range). Presently configured print cartridges do not provide an adequate way to dissipate the current path of the RF high voltage burst to return to a grounding source. Some of this current is returned through an array of secondary electrodes, normally called the finger electrodes. Most of the current is returned to ground potential through capacitive coupling with the mechanical substrate, and therefore can meander through other mechanical rigidifying structures of the print engine. This can make this structure into a radiating antenna structure, which can cause stray electrical noise, which interferes with other sensitive devices, such as data system lines and low voltage controlling electronics. Use of an intermediary conducting plane according to the invention yields a more direct electrical path to control and direct the RF currents back to ground.
The standard print cartridge used in the majority of electron beam printers used today is based on the 3-electrode cartridge as originally taught in U.S. Pat. No. 4,160,257. This patent is based on the earlier 2-electrode print cartridge of U.S. Pat. No. 4,155,093. This patent teaches a method of generating ions in air by applying an alternating potential between first and second electrodes on opposing sides of a solid dielectric member. The second electrode has an edge surface exposed to the air, which is opposed to the first electrode where electrical discharges produce ions. The patent describes the use of alternating potentials between 60 Hz and 4 mHz. The first electrode is commonly referred to as the RF drive line (RF--radio frequency) and the second electrode, the finger electrode. The solid dielectric material between the opposing electrodes is typically mica or a form of deposited dielectric paste. The alternating potential RF burst typically has an amplitude of 1.5-2.0 kilovolts at 500 kHz frequency with pulse durations from 20 to 50 microseconds.
U.S. Pat. No. 4,160,257, teaches the use of a third electrode structure (the screen electrode) to shape or focus the ionic beam which produces the electrostatic image. Mention is made of a driving RF potential with an amplitude of 1.0 kV at a frequency of 500 kHz. These cited patents only teach the basic electrode structure, function, and approximate configurations. Nothing is taught pertaining to the current flowing within the system or the mounting structure, which would serve as a mechanical platform and also a ground plane, which would react with the driving potentials electrically. In U.S. Pat. No. 4,408,214 (the disclosure of which is hereby incorporated by reference herein), a method and apparatus are described for the enhanced performance of the print cartridge while operating at elevated temperatures. A mounting block is described adjacent to the RF drive electrode to prevent heat build-up. This mounting block is described as being made of aluminum or stainless steel. Attached to the mounting block is a heating element which can raise the temperature of the cartridge structure while being controlled by a thermocouple device mounted in the region of ionic production.
Enhanced descriptions of print cartridge structure are taught in U.S. Pat. Nos. 4,679,060 and 4,745,421. These both describe a print cartridge with a stiff spine attached to the cartridge substrate to make the entire structure rigid. The substrate is now used to create a flat frame of reference and also serve as a handle.
Driving and bias potentials are often mentioned in their relationships to the cartridge electrodes, but a descriptive illustration of the electrical layout is taught in U.S. Pat. No. 4,494,129 (the disclosure of which is hereby incorporated by reference herein). Described are the basic illustrative paths for the RF oscillator alternating potential, finger electrode drivers, and the screen electrode. U.S. Pat. Nos. 5,315,324 and 5,014,076 (the disclosures of which are hereby incorporated by reference herein) teach the most recent knowledge relating to the function of the print cartridge and how charge carriers are generated to form an electrostatic latent image on a rotary dielectric member.
Through all of the descriptions in the above patents, nothing is disclosed concerning the need for the return path of the RF drive line voltage to ground potential. The current commercial Midax 300 print cartridges used by Moore U.S.A. of Lake Forest, Ill., are all made with an intermediary conducting plane made of copper, whose purpose is to dissipate the localized heat concentration points in the active areas of the cartridge. No mention has ever been made of its electrical coupling to the rest of the cartridge, however, and this layer is electrically isolated from ground potential within the machine and may or may not have enough capacitive coupling to affect the RF return current path.
Conventional electron beam imaging cartridge assemblies have a voltage drop that is developed across ground, power, control, or data lines that share current with a twelve inch piece of 20 gauge wire. On the right side printed circuit board (PCB) current path 3 amps of current are coupled to the left side of the finger electrode and on the left side of the PCB current path the current path is not well defined. When the current path hits the printer frame there is no predictability on exactly what path it is going to take. The traditional path of the current in an amp 8 inch DPI card which is via the fingers to the PCD capacitance, the left screen connection, through the screen, and then connecting to the right finger capacitance to the source generator. When using a 600 DPI, 18 inch, cartridge a screen electrode can no longer be used for a current carrying conductor since it is split into four sections that are connected with a high resistive epoxy that cannot handle 3 amps of current. If the screen were one piece it still would be risky to run current through it because of the voltage gradient that would be developed across. Although the screen electrode is not a 20 gauge wire it will still develop about .+-.10 volts end to end due to its inductance. Therefore, if the screen is an RF circuit it will cause significant problems. All of these difficulties ultimately end up causing stray electrical noise, making effective operation of the electron beam printed far from optimum.
According to the present invention the problems, as described above, with respect to conventional electron beam printers has been solved utilizing shielding isolated from the cartridge frame (also called a handle) and connected to each cluster of RF connections found at each corner of the cartridge. The shielding provides a defined path for the RF return currents, and effectively intercepts parasitic capacitance to the frame/handle.
According to one aspect of the present invention an electron beam imaging cartridge assembly is provided comprising the following components: A mechanical cartridge frame at least partially of electrically conductive material, and connected to electrical ground. An ion generator laminate, including electrodes, for generating electron printing beams. A plurality of RF generators connected to the ion generator laminate. Shielding of electrically conductive material connected by an electrical insulator to the mechanical cartridge frame, and connected between the laminate and the mechanical cartridge frame. And a plurality of electrical connections between the RF generators and the shielding which provide a defined path for RF return currents and intercept parasitic capacitance to the mechanical cartridge frame.
Typically the mechanical cartridge frame/handle comprises an active area and left and right sides, and the shielding is provided on and electrically insulated from all of the active area and the left and right sides of the mechanical cartridge frame. The shielding may comprise a copper layer, and the electrical insulator for connecting the shielding to the frame/handle may be any suitable conventional insulator or insulators (one piece, layered, etc.), the details thereof not being critical.
Typically the laminate includes left and right finger electrodes connected to left and right drivers, respectively, on left and right driver boards, respectively; and the left and right drivers are operatively substantially directly electrically connected to the electrical connections. Alternatively, and more desirably, the left and right drivers are electrically connected to the electrical connections to the shielding substantially only through the RF generators. Also, the left and right drivers are connected to logic control, and the logic controls are preferably electrically connected to the electrical connections to the shielding substantially only through the RF generators.
Typically, the mechanical cartridge frame is constructed of aluminum where connected to the shielding through the electrical insulation, and where connected to ground. A continuous path of aluminum is provided between the connection to the shielding, and the connection to ground. Typically, the laminate includes the screen electrode, and the screen electrode is not in an RF return current path.
According to another aspect of the present invention an electron beam printer cartridge subassembly is provided comprising: A mechanical cartridge frame at least in part of electrically conductive material connected to electrical ground, and comprising an active area and left and right sides; and shielding of electrically conductive material connected through an electrical insulator to all of the active area and left and right sides of the mechanical cartridge frame. The shielding typically comprises a copper layer, and the mechanical cartridge frame is preferably constructed of aluminum, as described above.
According to another aspect of the present invention there is provided a method of minimizing ground current through a printer frame in an electron beam printer having a mechanical cartridge frame at least partially of electrically conductive material, and connected to electrical ground; an ion generator laminate, including electrodes, for generating electron printing beams; and a plurality of RF generators connected to the ion generator laminate. The method comprises: (a) Mounting shielding of electrically conductive material connected by an electrical insulator to the mechanical cartridge frame. (b) Connecting the shielding between the laminate and the mechanical cartridge frame. And (c) providing a plurality of electrical connections between the RF generators and the shielding which provide a defined path for RF return currents to the RF generators, and which intercept parasitic capacitance to the mechanical cartridge frame.
Typically, the laminate includes left and right finger electrodes connected to left and right drivers, respectively, and left and right driver boards, respectively; and the method further comprises (d) electrically connecting the left and right drivers to the plurality of electrical connections substantially only through the RF generators. The invention is highly advantageous compared to conventional print cartridges. Also according to the present invention (a)-(d) are practiced to reduce the hybrid load capacitance by at least about 1/2, decrease the finger electrode rise and fall times by at least about 1/2, and reduce the unswitched ground currents through the cartridge frame by at least about 15 db, compared to if (a)-(d) are not practiced.
By utilizing the invention it is possible to effectively construct a 600 DPI, 18 inch, electron beam printer imaging cartridge assemblies. It is a primary object of the present invention to construct such cartridge assemblies and associated subassemblies, and to utilize a method of utilization thereof which minimize the electrical noise which can interfere with other sensitive devices associated with an electronic beam printer. This and other objects of the invention will become clear from a detailed inspection of the invention and from the appended claims.